1. Field of the Invention
The present invention relates to carbon-coated optical fibers and apparatus for producing same.
2. Prior Art
Quartz-based optical fibers have been widely used for communications cables. Hydrogen coming into contact with these fibers can diffuse through them, and the molecular vibrations of the hydrogen lead to greater absorption losses. In addition, the hydrogen may react with P.sub.2 O.sub.3, GeO.sub.2, or B.sub.2 O.sub.3, which are contained in the fiber as dopants, and forming compounds with one or more OH groups. Absorption by the OH group also increases absorption losses. One way to solve these problems is to add a liquid-phase composition which can absorb hydrogen in the fiber (Unexamined Japanese Patent Publication No. 61-251808). However, this method is impractical: the produced fiber has a limited capacity for hydrogen absorption and is structurally complex. Corning Glass (International Wire & Cable Symposium Proceedings 1987, pages 241-244, and JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 6, No. 2, Feb. 1988 , pages 240-244) and AT&T ELECTRONICS LETTERS, 13th Oct. 1988 Vol. 24, No. 21, pages 1323-1324, and OFC '88/TUESDAY AFTERNOON/23 ) have recently disclosed that coating the fiber with carbon by chemical vapor deposition (CVD) can enhance its resistance to hydrogen.
The hydrogen-resistance characteristics of this carbon coating and the mechanical properties of the carbon-coated fiber depend greatly on the carbon source and on deposition conditions. At present, the CVD process cannot yet produce optical fibers that are sufficiently hydrogen-resistant and mechanically strong.